Reverberation generation for headphone virtualization

ABSTRACT

The present disclosure relates to reverberation generation for headphone virtualization. A method of generating one or more components of a binaural room impulse response (BRIR) for headphone virtualization is described. In the method, directionally-controlled reflections are generated, wherein directionally-controlled reflections impart a desired perceptual cue to an audio input signal corresponding to a sound source location. Then at least the generated reflections are combined to obtain the one or more components of the BRIR. Corresponding system and computer program products are described as well.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/492,683, filed Oct. 4, 2021, which is a division of U.S. applicationSer. No. 16/986,308, filed Aug. 6, 2020, now U.S. Pat. No. 11,140,501,which is continuation of U.S. application Ser. No. 16/510,849 filed Jul.12, 2019, now U.S. Pat. No. 10,750,306, which is continuation of U.S.application Ser. No. 16/163,863 filed Oct. 18, 2018, now U.S. Pat. No.10,382,875, which is continuation of U.S. application Ser. No.15/550,424 filed Aug. 11, 2017, now U.S. Pat. No. 10,149,082, which isU.S. national phase of International Application No. PCT/US2016/017594filed Feb. 11, 2016, which claims priority to U.S. ProvisionalApplication No. 62/117,206 filed 17 Feb. 2015, Chinese PatentApplication No. 201510077020.3 filed 12 Feb. 2015 and ChineseApplication No. 201610081281.7 filed 5 Feb. 2016, each of which isincorporated by reference in its entirety.

TECHNOLOGY

Embodiments of the present disclosure generally relate to audio signalprocessing, and more specifically, to reverberation generation forheadphone virtualization.

BACKGROUND

In order to create a more immersive audio experience, binaural audiorendering can be used so as to impart a sense of space to 2-channelstereo and multichannel audio programs when presented over headphones.Generally, the sense of space can be created by convolvingappropriately-designed Binaural Room Impulse Responses (BRIRs) with eachaudio channel or object in the program, wherein the BRIR characterizestransformations of audio signals from a specific point in a space to alistener's ears in a specific acoustic environment. The processing canbe applied either by the content creator or by the consumer playbackdevice.

An approach of virtualizer design is to derive all or part of the BRIRsfrom either physical room/head measurements or room/head modelsimulations. Typically, a room or room model having very desirableacoustical properties is selected, with the aim that the headphonevirtualizer can replicate the compelling listening experience of theactual room. Under the assumption that the room model accuratelyembodies acoustical characteristics of the selected listening room, thisapproach produces virtualized BRIRs that inherently apply the auditorycues essential to spatial audio perception. Auditory cues may, forexample, include interaural time difference (ITD), interaural leveldifference (ILD), interaural crosscorrelation (IACC), reverberation time(e.g., T60 as a function of frequency), direct-to-reverberant (DR)energy ratio, specific spectral peaks and notches, echo density and thelike. Under ideal BRIR measurements and headphone listening conditions,binaural audio renderings of multichannel audio files based on physicalroom BRIRs can sound virtually indistinguishable from loudspeakerpresentations in the same room.

However, a drawback of this approach is that physical room BRIRs canmodify the signal to be rendered in undesired ways. When BRIRs aredesigned with adherence to the laws of room acoustics, some of theperceptual cues that lead to a sense of externalization, such asspectral combing and long T60 times, also cause side-effects such assound coloration and time smearing. In fact, even top-quality listeningrooms will impart some side-effects to the rendered output signal thatare not desirable for headphone reproduction. Furthermore, thecompelling listening experience that can be achieved during listening tobinaural content in the actual measurement room is rarely achievedduring listening to the same content in other environments (rooms).

SUMMARY

In view of the above, the present disclosure provides a solution forreverberation generation for headphone virtualization.

In one aspect, an example embodiment of the present disclosure providesa method of generating one or more components of a binaural room impulseresponse (BRIR) for headphone virtualization. In the method,directionally-controlled reflections are generated, wherein thedirectionally-controlled reflections impart a desired perceptual cue toan audio input signal corresponding to a sound source location, and thenat least the generated reflections are combined to obtain the one ormore components of the BRIR.

In another aspect, another example embodiment of the present disclosureprovides a system of generating one or more components of a binauralroom impulse response (BRIR) for headphone virtualization. The systemincludes a reflection generation unit and a combining unit. Thereflection generation unit is configured to generatedirectionally-controlled reflections that impart a desired perceptualcue to an audio input signal corresponding to a sound source location.The combining unit is configured to combine at least the generatedreflections to obtain the one or more components of the BRIR.

Through the following description, it would be appreciated that, inaccordance with example embodiments of the present disclosure, a BRIRlate response is generated by combining multiple synthetic roomreflections from directions that are selected to enhance the illusion ofa virtual sound source at a given location in space. The change inreflection direction imparts an IACC to the simulated late response thatvaries as a function of time and frequency. IACC primarily affects humanperception of sound source externalization and spaciousness. It can beappreciated by those skilled in the art that in example embodimentsdisclosed herein, certain directional reflection patterns can convey anatural sense of externalization while preserving audio fidelityrelative to prior-art methods. For example, the directional pattern canbe of an oscillatory (wobble) shape. In addition, by introducing adiffuse directional component within a predetermined range of azimuthsand elevations, a degree of randomness is imparted to the reflections,which can heighten the sense of naturalness. In this way, the methodaims to capture the essence of a physical room without its limitations.

A complete virtualizer can be realized by combining multiple BRIRs, onefor each virtual sound source (fixed loudspeaker or audio object). Inaccordance with the first example above, each sound source has a uniquelate response with directional attributes that reinforce the soundsource location. A key advantage of this approach is that a higherdirect-to-reverberation (DR) ratio can be utilized to achieve the samesense of externalization as conventional synthetic reverberationmethods. The use of higher DR ratios leads to fewer audible artifacts inthe rendered binaural signal, such as spectral coloration and temporalsmearing.

DESCRIPTION OF DRAWINGS

Through the following detailed description with reference to theaccompanying drawings, the above and other objectives, features andadvantages of embodiments of the present disclosure will become morecomprehensible. In the drawings, several example embodiments of thepresent disclosure will be illustrated in an example and non-limitingmanner, wherein:

FIG. 1 is a block diagram of a system of reverberation generation forheadphone virtualization in accordance with an example embodiment of thepresent disclosure;

FIG. 2 illustrates a diagram of a predetermined directional pattern inaccordance with an example embodiment of the present disclosure;

FIGS. 3A and 3B illustrate diagrams of short-time apparent directionchanges over time for well and poorly externalizing BRIR pairs for leftand right channel loudspeakers, respectively;

FIG. 4 illustrates a diagram of a predetermined directional pattern inaccordance with another example embodiment of the present disclosure;

FIG. 5 illustrates a method for generating a reflection at a givenoccurrence time point in accordance with an example embodiment of thepresent disclosure;

FIG. 6 is a block diagram of a general feedback delay network (FDN);

FIG. 7 is a block diagram of a system of reverberation generation forheadphone virtualization in an FDN environment in accordance withanother example embodiment of the present disclosure;

FIG. 8 is a block diagram of a system of reverberation generation forheadphone virtualization in an FDN environment in accordance with afurther example embodiment of the present disclosure;

FIG. 9 is a block diagram of a system of reverberation generation forheadphone virtualization in an FDN environment in accordance with astill further example embodiment of the present disclosure;

FIG. 10 is a block diagram of a system of reverberation generation forheadphone virtualization for multiple audio channels or objects in anFDN environment in accordance with an example embodiment of the presentdisclosure;

FIG. 11A/11B are block diagrams of a system of reverberation generationfor headphone virtualization for multiple audio channels or objects inan FDN environment in accordance with another example embodiment of thepresent disclosure;

FIG. 12A/12B are block diagrams of a system of reverberation generationfor headphone virtualization for multiple audio channels or objects inan FDN environment in accordance with a further example embodiment ofthe present disclosure;

FIG. 13 is a block diagram of a system of reverberation generation forheadphone virtualization for multiple audio channels or objects in anFDN environment in accordance with a still further example embodiment ofthe present disclosure;

FIG. 14 is a flowchart of a method of generating one or more componentsof a BRIR in accordance with an example embodiment of the presentdisclosure; and

FIG. 15 is a block diagram of an example computer system suitable forimplementing example embodiments of the present disclosure.

Throughout the drawings, the same or corresponding reference symbolsrefer to the same or corresponding parts.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Principles of the present disclosure will now be described withreference to various example embodiments illustrated in the drawings. Itshould be appreciated that depiction of these embodiments is only toenable those skilled in the art to better understand and furtherimplement the present disclosure, not intended for limiting the scope ofthe present disclosure in any manner.

In the accompanying drawings, various embodiments of the presentdisclosure are illustrated in block diagrams, flow charts and otherdiagrams. Each block in the flowcharts or block may represent a module,a program, or a part of code, which contains one or more executableinstructions for performing specified logic functions. Although theseblocks are illustrated in particular sequences for performing the stepsof the methods, they may not necessarily be performed strictly inaccordance with the illustrated sequence. For example, they might beperformed in reverse sequence or simultaneously, depending on the natureof the respective operations. It should also be noted that blockdiagrams and/or each block in the flowcharts and a combination ofthereof may be implemented by a dedicated hardware-based system forperforming specified functions/operations or by a combination ofdedicated hardware and computer instructions.

As used herein, the term “includes” and its variants are to be read asopen-ended terms that mean “includes, but is not limited to.” The term“or” is to be read as “and/or” unless the context clearly indicatesotherwise. The term “based on” is to be read as “based at least in parton.” The term “one example embodiment” and “an example embodiment” areto be read as “at least one example embodiment.” The term “anotherembodiment” is to be read as “at least one other embodiment”.

As used herein, the term “audio object” or “object” refers to anindividual audio element that exists for a defined duration of time inthe sound field. An audio object may be dynamic or static. For example,an audio object may be human, animal or any other object serving as asound source in the sound field. An audio object may have associatedmetadata that describes the location, velocity, trajectory, height, sizeand/or any other aspects of the audio object. As used herein, the term“audio bed” or “bed” refers to one or more audio channels that are meantto be reproduced in pre-defined, fixed locations. As used herein, theterm “BRIR” refers to the Binaural Room Impulse Responses (BRIRs) witheach audio channel or object, which characterizes transformations ofaudio signals from a specific point in a space to listener's ears in aspecific acoustic environment. Generally speaking, a BRIR can beseparated into three regions. The first region is referred to as thedirect response, which represents the impulse response from a point inanechoic space to the entrance of the ear canal. This direct response istypically of around 5 ms duration or less, and is more commonly referredto as the Head-Related Transfer Function (HRTF). The second region isreferred to as early reflections, which contains sound reflections fromobjects that are closest to the sound source and a listener (e.g. floor,room walls, furniture). The third region is called the late response,which includes a mixture of higher-order reflections with differentintensities and from a variety of directions. This third region is oftendescribed by stochastic parameters such as the peak density, modeldensity, energy-decay time and the like due to its complex structures.The human auditory system has evolved to respond to perceptual cuesconveyed in all three regions. The early reflections have a modesteffect on the perceived direction of the source but a stronger influenceon the perceived timbre and distance of the source, while the lateresponse influences the perceived environment in which the sound sourceis located. Other definitions, explicit and implicit, may be includedbelow.

As mentioned hereinabove, in a virtualizer design derived from a room orroom model, the BRIRs have properties determined by the laws ofacoustics, and thus the binaural renders produced therefrom contain avariety of perceptual cues. Such BRIRs can modify the signal to berendered over headphones in both desirable and undesirable ways. In viewof this, in embodiments of the present disclosure, there is provided anovel solution of reverberation generation for headphone virtualizationby lifting some of the constraints imposed by a physical room or roommodel. One aim of the proposed solution is to impart in a controlledmanner only the desired perceptual cues into a synthetic early and lateresponse. Desired perceptual cues are those that convey to listeners aconvincing illusion of location and spaciousness with minimal audibleimpairments (side effects). For example, the impression of distance fromthe listener's head to a virtual sound source at a specific location maybe enhanced by including room reflections in the early portion of thelate response having direction of arrivals from a limited range ofazimuths/elevations relative to the sound source. This imparts aspecific IACC characteristic that leads to a natural sense of spacewhile minimizing spectral coloration and time-smearing. The inventionaims to provide a more compelling listener experience than conventionalstereo by adding a natural sense of space while substantially preservingthe original sound mixer's artistic intent.

Hereinafter, reference will be made to FIGS. 1 to 9 to describe someexample embodiments of the present disclosure. However, it should beappreciated that these descriptions are made only for illustrationpurposes and the present disclosure is not limited thereto.

Reference is first made to FIG. 1 , which shows a block diagram of aone-channel system 100 for headphone virtualization in accordance withone example embodiment of the present disclosure. As shown, the system100 includes a reflection generation unit 110 and a combining unit 120.The generation unit 110 may be implemented by, for example, a filteringunit 110.

The filtering unit 110 is configured to convolve a BRIR containingdirectionally-controlled reflections that impart a desired perceptualcue with an audio input signal corresponding to a sound source location.The output is a set of left- and right-ear intermediate signals. Thecombining unit 120 receives the left- and right-ear intermediate signalsfrom the filtering unit 110 and combines them to form a binaural outputsignal.

As mentioned above, embodiments of the present disclosure are capable ofsimulating the BRIR response, especially the early reflections and thelate response to reduce spectral coloration and time-smearing whilepreserving naturalness. In embodiments of the present disclosure, thiscan be achieved by imparting directional cues into the BRIR response,especially the early reflections and the late response in a controlledmanner. In other words, direction control can be applied to thesereflections. Particularly, the reflections can be generated in such away that they have a desired directional pattern, in which directions ofarrival have a desired change as function of time.

The example embodiments disclosed herein provide that a desirable BRIRresponse can be generated using a predetermined directional pattern tocontrol the reflection directions. In particular, the predetermineddirectional pattern can be selected to impart perceptual cues thatenhance the illusion of a virtual sound source at a given location inspace. As one example, the predetermined directional pattern can be of awobble function. For a reflection at a given point in time, the wobblefunction determines wholly or in part the direction of arrival (azimuthand/or elevation). The change in reflection directions creates asimulated BRIR response with IACC that varies as a function of time andfrequency. In addition to the ITD, the ILD, the DR energy ratio, and thereverberation time, the IACC is also one of the primary perceptual cuesthat affect listener's impression of sound source externalization andspaciousness. However, it is not well-known in the art which specificevolving patterns of IACC across time and frequency are most effectivefor conveying a sense of 3-dimensional space while preserving the soundmixer' artistic intent as much as possible. Example embodimentsdescribed herein provide that specific directional reflections patterns,such as the wobble shape of reflections, can convey a natural sense ofexternalization while preserving audio fidelity relative to conventionalmethods.

FIG. 2 illustrates a predetermined directional pattern in accordancewith an example embodiment of the present disclosure. In FIG. 2 a wobbletrajectory of synthesized reflections is illustrated, wherein each dotrepresents a reflection component with an associated azimuthaldirection, and the sound direction of the first arrival signal isindicated by the black square at the time origin. From FIG. 2 , it isclear that the reflection directions change away from the direction ofthe first arrival signal and oscillate around it while the reflectiondensity generally increases with time.

In BRIRs measured in rooms with good externalization, strong and welldefined directional wobbles are associated with good externalization.This can be seen from FIGS. 3A and 3B, which illustrate examples of theapparent direction changes when 4 ms segments from BRIRs with good andpoor externalization are auditioned by headphone listening.

From FIGS. 3A and 3B, it can be clearly seen that good externalizationis associated with strong directional wobbles. The short-termdirectional wobbles exist not only in the azimuthal plane but also inthe medial plane. This is true because reflections in a conventional6-surface room are a 3-dimensional phenomenon, not just a 2-dimensionalone. Therefore, reflections in a time interval of 10-50 ms may alsoproduce short-term directional wobbles in elevation. Therefore, theinclusion of these wobbles in BRIR pairs can be used to increaseexternalization.

Practical application of short-term directional wobbles for all thepossible source directions in an acoustic environment can beaccomplished via a finite number of directional wobbles to use for thegeneration of a BRIR pair with good externalization. This can be done,for example, by dividing up the sphere of all vertical and horizontaldirections for first-arrival sound directions into a finite number ofregions. A sound source coming from a particular region is associatedwith two or more short-term directional wobbles for that region togenerate a BRIR pair with good externalization. That is to say, thewobbles can be selected based on the direction of the virtual soundsource.

Based on analyses of room measurements, it can be seen that soundreflections typically first wobble in direction but rapidly becomeisotropic, thereby creating a diffuse sound field. Therefore, it isuseful to include a diffuse or stochastic component in creating a goodexternalizing BRIR pair with a natural sound. The addition ofdiffuseness is a tradeoff among the natural sound, externalization, andfocused source size. Too much diffuseness might create a very broad andpoor directionally defined sound source. On the other hand, too littlediffuseness can result in unnatural echoes coming from the sound source.As a result, a moderate growth of randomness in source direction isdesirable, which means that the randomness shall be controlled to acertain degree. In an embodiment of the present disclosure, thedirectional range is limited within a predetermined azimuths range tocover a region around the original source direction, which may result ina good tradeoff among naturalness, source width, and source direction.

FIG. 4 further illustrates a predetermined directional pattern inaccordance with another example embodiment of the present disclosure.Particularly, in FIG. 4 are illustrated reflection directions as afunction of time for an example azimuthal short-term directional wobblesand the added diffuse component for a center channel. The reflectiondirections of arrival initially emanate from a small range of azimuthsand elevations relative to the sound source, and then expand wider overtime. As illustrated in FIG. 4 , the slowly-varying directional wobblefrom FIG. 2 is combined with an increasing stochastic (random) directioncomponent to create diffuseness. The diffuse component as illustrated inFIG. 4 linearly grows to ±45 degrees at 80 ms, and the full range ofazimuths is only ±60 degrees relative to the sound source, compared to±180 degrees in a six-sided rectangular room. The predetermineddirectional pattern may also include a portion of reflections withdirection of arrival from below the horizontal plane. Such a feature isuseful for simulating ground reflections that are important to the humanauditory system for localizing front horizontal sound sources at thecorrect elevation.

In view of the fact that the addition of the diffuse componentintroduces further diffuseness, the resulting reflections and theassociated directions for the BRIR pair as illustrated in FIG. 4 canachieve better externalization. In fact, similar to the wobbles, thediffuse component can be also selected based on the direction of thevirtual sound source. In this way, it is possible to generate asynthetic BRIR that imparts the perceptual effect of enhancing thelistener's sense of sound source location and externalization.

These short-term directional wobbles usually cause the sounds in eachear to have the real part of the frequency dependent IACC to have strongsystematic variations in a time interval (for example, 10-50 ms) beforethe reflections become isotropic and uniform in the direction asmentioned earlier. As the BRIR evolves later in time, the IACC realvalues above about 800 Hz drop due to increased diffuseness of the soundfield. Thus, the real part of the IACC derived from left- and right-earresponses varies as a function of frequency and time. The use of thefrequency dependent real part has an advantage that it revealscorrelation and anti-correlation characteristics and it is a usefulmetric for virtualization.

In fact, there are many characteristics in the real part of the IACCthat create strong externalization, but the persistence of the timevarying correlation characteristics over a time interval (for example 10to 50 ms) may indicate good externalization. With example embodiments asdisclosed herein, it may produce the real part of IACCs having highervalues, which means a higher persistence of correlation (above 800 Hzand extending to 90 ms) than that would occur in a physical room. Thus,with example embodiments as disclosed herein it may obtain bettervirtualizers.

In an embodiment of the present disclosure, the coefficients forfiltering unit 110 can be generated using a stochastic echo generator toobtain the early reflections and late response with the transitionalcharacteristics described above. As illustrated in FIG. 1 the filteringunit can include delayers 111-1, . . . , 111-i, . . . , 111-k(collectively referred to as 111 hereinafter), and filters 112-0, 112-1,. . . , 112-i, . . . 112-k (collectively referred to as 112hereinafter). The delayers 111 can be represented by Z^(-ni), whereini=1 to k. The coefficients for filters 112 may be, for example, derivedfrom an HRTF data set, where each filter provides perceptual cuescorresponding to one reflection from a predetermined direction for boththe left ear and the right ear. As illustrated in FIG. 1 , in eachsignal line, there is a delayer and filter pair, which could generateone intermediate signal (e.g. reflection) from a known direction at apredetermined time. The combining unit 120 includes, for example, a leftsummer 121-L and a right summer 121-R. All left ear intermediate signalsare mixed in the left summer 121-L to produce the left binaural signal.Similarly, all right ear intermediate signals are mixed in the rightsummer 121-R to produce the right binaural signal. In such a way,reverberation can be generated from the generated reflections with thepredetermined directional pattern, together with the direct responsegenerated by the filter 112-0 to produce the left and right binauraloutput signal.

In an embodiment of the present disclosure, operations of the stochasticecho generator can be implemented as follows. First, at each time pointas the stochastic echo generator progresses along the time axis, anindependent stochastic binary decision is first made to decide whether areflection should be generated at the given time instant. Theprobability of a positive decision increases with time, preferablyquadratically, for increasing the echo density. That is to say, theoccurrence time points of the reflections can be determinedstochastically, but at the same time, the determination is made within apredetermined echo density distribution constraint so as to achieve adesired distribution. The output of the decision is a sequence of theoccurrence time points of the reflections (also called as echopositions), n₁, n₂, . . . , n_(k), which respond to the delay time ofthe delayers 111 as illustrated in FIG. 1 . Then, for a time point, if areflection is determined to be generated, an impulse responses pair willbe generated for the left ear and right ear according to the desireddirection. This direction can be determined based on a predeterminedfunction which represents directions of arrival as a function of time,such as a wobbling function. The amplitude of the reflection can be astochastic value without any further control. This pair of impulseresponses will be considered as the generated BRIR at that time instant.In PCT application WO2015103024 published on Jul. 9, 2015, it describesa stochastic echo generator in details, which is hereby incorporated byreference in its entirety.

For the illustration purpose, an example process for generating areflection at a given occurrence time point will be described next withreference to FIG. 5 to enable those skilled in the art to fullyunderstand and further implement the proposed solution in the presentdisclosure.

FIG. 5 illustrates a method for generating a reflection at a givenoccurrence time point (500) in accordance with an example embodiment ofthe present disclosure As illustrated in FIG. 5 the method 500 isentered at step 510, where a direction of the reflection d_(DIR) isdetermined based a predetermined direction pattern (for example adirection pattern function) and the given occurrence time point. Then,at step 520, the amplitude of the reflection d_(AMP) is determined,which can be a stochastic value. Next, filters such as HRTFs with thedesired direction are obtained at step 530. For example, HRTF_(L) andHRTF_(R) may be obtained for the left ear and the right ear,respectively. Particularly, the HRTFs can be retrieved from a measuredHRTF data set for particular directions. The measured HRTF data set canbe formed by measuring the HRTF responses offline for particularmeasurement directions. In such a way, it is possible to select a HRTFwith the desired direction from HRTFs data set during generating thereflection. The selected HRTFs correspond to filters 112 at respectivesignal lines as illustrated in FIG. 1 .

At step 540, the maximal average amplitudes of the HRTFs for the leftear and the right ear can be determined. Specifically, the averageamplitude of the retrieved HRTFs of the left ear and the right ear canbe first calculated respectively and then the maximal one of the averageamplitudes of the HRTFs of left ear and right ear is further determined,which can be represented as but not limited to:

Amp _(max)=max(|HRTF_(L)|,|HRTF_(R)|)  (Eq. 1)

Next, at step 550, the HRTFs for the left and right ears are modified.Particularly, the maximal average amplitudes of HRTFs for both the leftand the right ear are modified according to the determined amplituded_(AMP) In an example embodiment of the present disclosure, it can bemodified as hut not limited to:

$\begin{matrix}{{HRTF}_{LM} = {\frac{d_{AMP}}{{Amp}_{Max}}{HRTF}_{L}}} & ( {{{Eq}.2}A} )\end{matrix}$ $\begin{matrix}{{HRTF}_{RM} = {\frac{d_{AMP}}{{Amp}_{Max}}{HRTF}_{R}}} & ( {{{Eq}.2}B} )\end{matrix}$

As a result, two reflections with a desired directional component forthe left ear and the right ear respectively can be obtained at a giventime point, which are output from the respective filters as illustratedin FIG. 1 . The resulting HRTF_(LM) is mixed into the left ear BRIR as areflection for the left ear, while HRTF_(RM) is mixed into the right earBRIR as a reflection for the right ear. The process of generating andmixing reflections into the BRIR to create synthetic reverberationcontinues until the desired BRIR length is reached. The final BRIRincludes a direct response for left and right ears, followed by thesynthetic reverberation.

In the embodiments of the present disclosure disclosed hereinabove, theHRTF responses can be measured offline for particular measurementdirections so as to form an HRTF data set. Thus during generating ofreflections, the HRTF responses can be selected from the measured HRTFdata set according to the desired direction. Since an HRTF response inthe HRTF data set represents an HRTF response for a unit impulse signal,the selected HRTF will be modified by the determined amplitude d_(AMP)to obtain the response suitable for the determined amplitude. Therefore,in this embodiment of the present disclosure, the reflections with thedesired direction and the determined amplitude are generated byselecting suitable HRTFs based on the desired direction from the HRTFdata sets and further modifying the HRTFs in accordance with theamplitudes of the reflections.

However, in another embodiment of the present disclosure, the HRTFs forthe left and right ears HRTF_(L) and HRTF_(R) can be determined based ona spherical head model instead of selecting from a measured HRTF dataset. That is to say, the HRTFs can be determined based on the determinedamplitude and a predetermined head model. In such a way, measurementefforts can be saved significantly.

In a further embodiment of the present disclosure, the HRTFs for theleft and right ears HRTF_(L) and HRTF_(R) can be replaced by an impulsepair with similar auditory cues (For example, interaural time difference(ITD) and interaural level difference (ILD) auditory cues). That is tosay, impulse responses for two ears can be generated based on thedesired direction and the determined amplitude at the given occurrencetime point and broadband ITD and ILD of a predetermined spherical headmodel. The ITD and ILD between the impulse response pair can becalculated, for example, directly based on HRTF_(L) and HRTF_(R). Or,alternatively, the ITD and ILD between the impulse response pair can becalculated based on a predetermined spherical head model. In general, apair of all-pass filters, particularly multi-stage all-pass filters(APFs), may be applied to the left and right channels of the generatedsynthetic reverberation as the final operation of the echo generator. Insuch a way, it is possible to introduce controlled diffusion anddecorrelation effects to the reflections and thus improve naturalness ofbinaural renders produced by the virtualizer.

Although specific methods for generating a reflection at given timeinstant are described, it should be appreciated that the presentdisclosure is not limited thereto; instead, any of other appropriatemethods are possible to create similar transitional behavior. As anotherexample, it is also possible to generate a reflection with a desireddirection by means of, for example, an image model.

By progressing along the time axis, the reflection generator maygenerate reflections for a BRIR with controlled directions of arrival asa function of time.

In another embodiment of the present disclosure, multiple sets ofcoefficients for the filtering unit 110 can be generated so as toproduce a plurality of candidate BRIRs, and then a perceptually-basedperformance evaluation can be made (such as spectral flatness, degree ofmatch with a predetermined room characteristic, and so on) for examplebased on a suitably-defined objective function. Reflections from theBRIR with an optimal characteristic are selected for use in thefiltering unit 110. For example, reflections with early reflection andlate response characteristics that represent an optimal tradeoff betweenthe various BRIR performance attributes can be selected as the finalreflections. While in another embodiment of the present disclosure,multiple sets of coefficients for the filtering unit 110 can begenerated until a desirable perceptual cue is imparted. That is to say,the desirable perceptual metric is set in advance, and if it issatisfied, the stochastic echo generator will stop its operations andoutput the resulting reflections.

Therefore, in embodiments of the present disclosure, there is provided anovel solution for reverberation for headphone virtualization,particularly, a novel solution for designing the early reflection andreverberant portions of binaural room impulse responses (BRIRs) inheadphone virtualizers. For each sound source, a unique,direction-dependent late response will be used, and the early reflectionand the late response are generated by combining multiple synthetic roomreflections with directionally-controlled directions of arrival as afunction of time. By applying a direction control on the reflectionsinstead of using reflections measured based on a physical room orspherical head model, it is possible to simulate BRIR responses thatimpart desired perceptual cues while minimizing side-effects. In someembodiments of the present disclosure, the predetermined directionalpattern is selected so that illusion of a virtual sound source at agiven location in space is enhanced. Particularly, the predetermineddirectional pattern can be, for example, a wobble shape with anadditional diffuse component within a predetermined azimuth range. Thechange in reflection direction imparts a time-varying IACC, whichprovides further primary perceptual cues and thus conveys a naturalsense of externalization while preserving audio fidelity. In this way,the solution could capture the essence of a physical room without itslimitations.

In addition, the solution as proposed herein supports binauralvirtualization of both channel-based and object-based audio programmaterial using direct convolution or more computationally-efficientmethods. The BRIR for a fixed sound source can be designed offlinesimply by combining the associated direct response with adirection-dependent late response. The BRIR for an audio object can beconstructed on-the-fly during headphone rendering by combining thetime-varying direct response with the early reflections and the lateresponse derived by interpolating multiple late responses from nearbytime-invariant locations in space.

Besides, in order to implement the proposed solution in acomputationally-efficient manner, the proposed solution is also possibleto be realized in a feedback delay network (FDN), which will bedescribed hereinafter with reference to FIGS. 6 to 8 .

As mentioned, in conventional headphone virtualizers, the reverberationof the BRIRs is commonly divided into two parts: the early reflectionsand the late response. Such a separation of the BRIRs allows dedicatedmodels to simulate characteristics for each part of the BRIR. It isknown that the early reflections are sparse and directional, while thelate response is dense and diffusive. In such a case, the earlyreflections may be applied to an audio signal using a bank of delaylines, each followed by convolution with the HRTF pair corresponding tothe associated reflection, while the late response can be implementedwith one or more Feedback Delay Networks (FDN). The FDN can beimplemented using multiple delay lines interconnected by a feedback loopwith a feedback matrix. This structure can be used to simulate thestochastic characteristics of the late response, particularly theincrease of the echo density over time. It is computationally moreefficient compared to deterministic methods such as image model, andthus it is commonly used to derive the late response. For illustrationpurposes, FIG. 6 illustrates a block diagram of a general feedback delaynetwork in the prior art.

As illustrated in FIG. 6 , the virtualizer 600 includes an FDN withthree delay lines generally indicated by 611, interconnected by afeedback matrix 612. Each of delay lines 611 could output a time delayedversion of the input signal. The outputs of the delay lines 611 would besent to the mixing matrix 621 to form the output signal and at the sametime also fed into the feedback matrix 612, and feedback signals outputfrom the feedback matrix are in turn mixed with the next frame of theinput signal at summers 613-1 to 613-3. It is to be noted that only theearly and late responses are sent to the FDN and go through the threedelay lines, and the direct response is sent to the mixing matrixdirectly and not to the FDN and thus it is not a part of the FDN.

However, one of the drawbacks of the early-late response lies in asudden transition from the early response to the late response. That is,the BRIRs will be directional in the early response, but suddenlychanges to a dense and diffusive late response. This is certainlydifferent from a real BRIR and would affect the perceptual quality ofthe binaural virtualization. Thus, it is desirable if the idea asproposed in the present disclosure can be embodied in the FDN, which isa common structure for simulating the late response in a headphonevirtualizer. Therefore, there is provided another solution hereinafter,which is realized by adding a bank of parallel HRTF filters in front ofa feedback delay network (FDN). Each HRTF filter generates the left- andright-ear response corresponding to one room reflection. Detaileddescription will be made with reference to FIG. 7 .

FIG. 7 illustrates a headphone virtualizer based on FDN in accordancewith an example embodiment of the present disclosure. Different fromFIG. 6 , in the virtualizer 700, there are further arranged filters suchas HRTF filters 714-0, 714-1, . . . 714-i . . . 714-k and delay linessuch delay lines 715-0, 715-1, 715-i, . . . 715-k. Thus, the inputsignal will be delayed through delay lines 715-0, 715-1, 715-i, . . .715-k to output different time delayed versions of the input signal,which are then preprocessed by filters such as HRTF filters 714-0,714-1, . . . 714-i . . . 714-k before entering the mixing matrix 720 orthe FDN, particularly before signals fed back through at least onefeedback matrix are added. In some embodiments of the presentdisclosure, the delay value d₀(n) for the delay line 715-0, can be zeroin order to save the memory storage. In other embodiments of the presentdisclosure, the delay value d₀(n) can be set as a nonzero value so at tocontrol the time delay between the object and the listener.

In FIG. 7 , and the delay time of each of the delay lines andcorresponding HRTF filters can be determined based on the method asdescribed herein. Moreover, it will require a smaller number of filters(for example, 4, 5, 6, 7 or 8) and a part of the late response isgenerated through the FDN structure. In such a way, the reflections canbe generated in a computationally more efficient way. At the same time,it may ensure that:

-   -   The early part of the late response contains directional cues.    -   All inputs to the FDN structure are directional, which allows        outputs of the FDN to be directionally diffusive. Since the        outputs of the FDN are now created by the summation of the        directional reflections, it is more similar to a real-world BRIR        generation, which means a smooth transition from the directional        reflections and thus diffusive reflections are ensured.    -   The direction of the early part of the late response can be        controlled to have a predetermined direction of arrival.        Different from the early reflections generated by the image        model, the direction of the early part of the late response may        be determined by different predetermined directional functions        which represent characteristics of the early part of the late        response. As an example, the aforementioned wobbling functions        may be employed here to guide the selection process of the HRTF        pairs _((h) _(i) _((n), 0≤i≤k))

Thus, in the solution as illustrated in FIG. 7 , directional cues areimparted to the audio input signal by controlling the direction of theearly part of the late response so that they have a predetermineddirection of arrival. Accordingly, a soft transition is achieved, whichis from fully directional reflections (early reflections that will beprocessed by the model discussed earlier) to semi-directionalreflections (the early part of the late response that will have theduality between directional and diffusive), and finally evolves to fullydiffusive reflections (the reminder of the late response), instead of ahard directional to diffusive transition of the reflections in thegeneral FDN.

It shall be understood that, the delay lines 715-0, 715-1, 715-i, . . .,715-k can also be built in the FDN for implementation efficiency.Alternatively, they can also be tapped delay lines (a cascade ofmultiple delay units with HRTF filters at the output of each one), toachieve the same function as shown in FIG. 7 with less memory storage.

In addition, FIG. 8 further illustrates a headphone virtualizer 800based on FDN in accordance with another example embodiment of thepresent disclosure. The difference from the headphone virtualizer asillustrated in FIG. 7 lies in that, instead of one feedback matrix 712,two feedback matrixes 812L and 812R are used for the left ear and theright ear, respectively. In such a way, it could be more computationallyefficient. Regarding the bank of delay lines 811, and summers 813-1L to813-kL, 813-1R to 813 kR, 814-0 to 814-k, these components arefunctionally similar to bank of delay lines 711, and summers 713-1L to713-kL, 713-1R to 713 kR, 714-0 to 714-k. That is, these componentsfunction in a matter such that they mix with the next frame of the inputsignal as shown in FIGS. 7 and 8 , respectively, as such, their detaileddescription will be omitted for the purpose of simplification. Inaddition, delay lines 815-0, 815-1, 815-i, . . . 815-k also function ina similar way to delay lines 715-0, 715-1, 715-i, . . . 715-k and thusomitted herein.

FIG. 9 further illustrates a headphone virtualizer 900 based on FDN inaccordance with a further example embodiment of the present disclosure.Different from the headphone virtualizer as illustrated in FIG. 7 , inFIG. 9 , delay lines 915-0, 915-1, 915-i, . . . 915-k and HRTF filters914-0, 914-1, . . . 914-i . . . 914-k are not connected with the FDNserially but connected therewith parallelly. That is to say, the inputsignal will be delayed through delay lines 915-0, 915-1, 915-i, . . .915-k and be preprocessed by HRTF filters 914-0, 914-1, . . . 914-i . .. 914-k and then sent to the mixing matrix, in which the pre-proposedsignals will be mixed with signals going through the FDN. Thus, theinput signals pre-processed by HRTF filters are not sent to the FDNnetwork but sent to the mixing matrix directly.

It should be noted that the structures illustrated in FIGS. 7 to 9 arefully compatible with assorted audio input formats including, but notlimited to, channel-based audio as well as object-based audio. In fact,the input signals may be any of a single channel of the multichannelaudio signal, a mixture of the multichannel signal, a signal audioobject of the object-based audio signal, a mixture of the object-basedaudio signal, or any possible combinations thereof.

In a case of multiple audio channels or objects, each channel or eachobject can be arranged with a dedicated virtualizer for processing theinput signals. FIG. 10 illustrates a headphone virtualizing system 1000for multiple audio channels or objects in accordance with an exampleembodiment of the present disclosure. As illustrated in FIG. 10 , inputsignals from each audio channel or object will be processed by aseparate virtualizer such as virtualizer 700, 800, or 900. The leftoutput signals from each of the virtualizer can be summed up so as toform the final left output signals, and the right output signals fromeach of the virtualizer can be summed up so as to form the final rightoutput signals.

The headphone virtualizing system 1000 can be used especially when thereare enough computing resources; however, for application with limitedcomputing resources, it requires another solution since computingresources required by the system 1000 will be unacceptable for theseapplications. In such a case, it is possible to obtain a mixture of themultiple audio channels or objects with their corresponding reflectionsbefore the FDN or in parallel with the FDN. In other words, audiochannels or objects with their corresponding reflections can beprocessed and converted into a single audio channel or object signal.

FIGS. 11A/B illustrates a headphone virtualizing system 1100 formultiple audio channels or objects in accordance with another exampleembodiment of the present disclosure. Different from that illustrated inFIG. 7 , in the system 1100, there are provided m reflection delay andfilter networks1115-1 to 1115-m for m audio channels or objects. Eachreflection delay and filter network 1115-1, . . . or 1115-m includes k+1delay lines and k+1 HRTF filters, where one delay line and one HRTFfilter are used for the direct response and other delay lines and otherHRTF filter are used for the early and late responses. As illustrated,for audio channel or object 1, an input signal goes through the firstreflection delay and filter network 1115-1, that is to say, the inputsignal is first delayed through delay lines1115-1,0, 1115-1,1, 1115-1,i,. . . , 1115-1, k and then are filtered by HRTF filters 1114-1,0,1114-1,1, . . . 1114-1,i . . . 1114-1,k; for audio channel or object m,an input signal goes through the m-th reflection delay and filternetwork 1115-m, that is to say, the input signal is first delayedthrough delay lines 1115-m,0, 1115-m,1, 1115-m,i, 1115-m,k and then thenare filtered by HRTF filters 1114-m,0, 1114-m,1, . . . 1114-m,i . . .1114-m,k. The left output signal from each of HRTF filters 1114-1,1, . .. ,1114-1,i, . . . ,1114-1,k, and 1114-1,0, in the reflection delay andfilter network 1115-1 are combined with left output signals fromcorresponding HRTF filters in other reflection delay and filter networks1115-2 to 1115-m, the obtained left output signals for early and lateresponses are sent to summers in FDN and the left output signal for thedirect response is sent to the mixing matrix directly. Similarly, theright output signal from each of HRTF filters 1114-1,1, . . . ,1114-1,i,. . . ,1114-1,k, and 1114-1,0, in the reflection delay and filternetwork 1115-1 are combined with right output signals from correspondingHRTF filters in other reflection delay and filter networks 1115-2 to1115-m and the obtained right output signals for early and lateresponses are sent to summers in FDN and the right output signal as thedirect response is sent to the mixing matrix directly.

FIGS. 12A/12B illustrates a headphone virtualizing system 1200 formulti-channel or multi-object in accordance with a further exampleembodiment of the present disclosure. Different from FIGS. 11A/11B, thesystem 1200 is built based on the structure of system 900 as illustratedin FIG. 9 . In the system 1200, there are also provided m reflectiondelay and filter networks1215-1 to 1215-m for m audio channels orobjects. The reflection delay and filter networks1215-1 to 1215-m aresimilar to those illustrated in FIGS. 11A/11B and the difference lies inthat k+1 summed left output signals and k+1 summed right output signalsfrom reflection delay and filter networks 1215-1 to 1215-m are directlysent to the mixing matrix 1221 and none of them are sent to the FDN; andat the same time, input signals from m audio channels or objects aresummed up to obtain a downmixed audio signal which is provided to theFDN and further sent to the mixing matrix 1221. Thus, in system 1200,there is provided a separate reflection delay and filter network foreach audio channel or object and the output of the delay and filternetworks are summed up and then mixed with those from FDN. In such acase, each early reflection will appear once in the final BRIR and hasno further effect on the left/right output signals and the FDN willprovide a purely diffuse output.

In addition, in FIG. 12A/12B, the summers between the reflection delayand filter networks 1215-1 to 1215-m and the mixing matrix can also beremoved. That is to say, the outputs of the delay and filter networkscan be directly provided to the mixing matrix 1221 without summing andmixed with output from FDN.

In a still further embodiment of the present disclosure, the audiochannels or objects may be down mixed to form a mixture signal with adomain source direction and in such a case the mixture signal can bedirectly input to the system 700, 800 or 900 as a single signal. Next,reference will be made to FIG. 13 to describe the embodiment, whereinFIG. 13 illustrates a headphone virtualizing system 1300 for multipleaudio channels or objects in accordance with a still further exampleembodiment of the present disclosure.

As illustrated in FIG. 13 , audio channels or objects 1 to m are firstsent to a downmixing and dominant source direction analysis module 1316.In the downmixing and dominant source direction analysis module 1316,audio channels or objects 1 to m will be further downmixed into an audiomixture signal through for example summing and the dominant sourcedirection can be further analyzed on audio channels or objects 1 to m toobtain the dominant source direction of audio channels or objects 1 tom. In such a way, it is possible to obtain a single channel audiomixture signal with a source direction for example in azimuth andelevation. The resulting single channel audio mixture signal can beinput into the system 700, 800 or 900 as a single audio channel orobject.

The dominant source direction can be analyzed in the time domain or inthe time-frequency domain by means of any suitable manners, such asthose already used in the existing source direction analysis methods.Hereinafter, for a purpose of illustration, an example analysis methodwill be described in the time-frequency domain.

As an example, in the time-frequency domain, the sound source of thea_(i)-th audio channel or object can be represented by a sound sourcevector a_(i)(n,k), which is a function of its azimuth μ_(i), elevationη_(i), and a gain variable g_(i), and can be given by:

${a_{i}( {n,k} )} = {{{g_{i}( {n,k} )} \cdot \begin{bmatrix}\vartheta_{i} \\\varepsilon_{i} \\\zeta_{i}\end{bmatrix}} = {{g_{i}( {n,k} )} \cdot \begin{bmatrix}{\cos{\mu_{i} \cdot \cos}\eta_{i}} \\{\sin{\mu_{i} \cdot \cos}\eta_{i}} \\{\sin\eta_{i}}\end{bmatrix}}}$

wherein k and n are frequency and temporal frame indices, respectively;g_(i)(n,k) represents the gain for this channel or object; [

_(i) ε_(i) ξ_(i)]^(T) is the unit vector representing the channel orobject location. The overall source level g_(s)(n,k) contributed by allof the speakers can be given by:

${g_{s}^{2}( {n,k} )} = {\lbrack {\sum\limits_{i = 1}^{k}{{g_{i}( {n,k} )} \cdot {\vartheta_{i}}}} \rbrack^{2} + \lbrack {\sum\limits_{i = 1}^{k}{{g_{i}( {n,k} )} \cdot {\varepsilon_{i}}}} \rbrack^{2} + \lbrack {\sum\limits_{i = 1}^{k}{{g_{i}( {n,k} )} \cdot {\xi_{i}}}} \rbrack^{2}}$

The single channel downmixed signal can be created by applying the phaseinformation e^(φ) chosen from the channel with the highest amplitude inorder to maintain phase consistence, which may be given by:

α(n,k)=√{square root over (g ²,(n,k)·eφ)}

The direction of the downmixed signal, presented by its azimuth 8 (n, k)and elevation ϕ(n,k), can then be given by:

${\tan{\theta( {n,k} )}} = \frac{\overset{k}{\sum\limits_{i = 1}}{{g_{i}( {n,k} )} \cdot \vartheta_{i}}}{\sum\limits_{i = 1}^{k}{{g_{i}( {n,k} )} \cdot \varepsilon_{i}}}$${\tan{\phi( {n,k} )}} = \frac{\sqrt{\lbrack {\sum\limits_{i = 1}^{k}{{g_{i}( {n,k} )} \cdot \vartheta_{i}}} \rbrack^{2} + \lbrack {\sum\limits_{i = 1}^{k}{{g_{i}( {n,k} )} \cdot \varepsilon_{i}}} \rbrack^{2}}}{\sum\limits_{i = 1}^{k}{{g_{i}( {n,k} )} \cdot \xi_{i}}}$

In such a way, the domain source direction for the audio mixture signalcan be determined. However, it can be understood that the presentdisclosure is not limited to the above-described example analysismethod, and any other suitable methods are also possible, for example,those in the time frequency.

It shall be understood that the mixing coefficients for early refectionin mixing matrix can be an identity matrix. The mixing matrix is tocontrol the correlation between the left output and the right output. Itshall be understood that all these embodiments can be implemented inboth time domain and frequency domain. For an implementation in thefrequency domain, the input can be parameters for each band and theoutput can be processed parameters for the band.

Besides, it is noted that the solution proposed herein can alsofacilitate the performance improvement of the existing binauralvirtualizer without any necessity of any structural modification. Thiscan be achieved by obtaining an optimal set of parameters for theheadphone virtualizer based on the BRIR generated by the solutionproposed herein. The parameter can be obtained by an optimal process.For example, the BRIR created by the solution proposed herein (forexample with regard to FIGS. 1 to 5 ) can set a target BRIR, then theheadphone virtualizer of interest is used to generate BRIR. Thedifference between the target BRIR and the generated BRIR is calculated.Then the generating of BRIR and the calculating of difference arerepeated until all possible combinations of the parameters are covered.Finally, the optimal set of parameters for the headphone virtualizer ofinterest would be selected, which can minimize the difference betweenthe target BRIR and the generated BRIR. The measurement of thesimilarity or difference between two BRIRs can be achieved by extractingthe perceptual cues from the BRIRs. For example, the amplitude ratiobetween left and right channels may be employed as a measure of thewobbling effect. In such a way, with the optimal set of parameters, eventhe existing binaural virtualizer might achieve a better virtualizationperformance without any structural modification.

FIG. 14 further illustrates a method of generating one or morecomponents of a BRIR in accordance with an example embodiment of thepresent disclosure.

As illustrated in FIG. 14 , the method 1400 is entered at step 1410,where the directionally-controlled reflections are generated, andwherein the directionally-controlled reflections can impart a desiredperceptual cue to an audio input signal corresponding to a sound sourcelocation. Then at step 1420, at least the generated reflections arecombined to obtain one or more components of the BRIR. In embodiments ofthe present disclosure, to avoid limitations of a particular physicalroom or room model, a direction control can be applied to thereflections. The predetermined direction of arrival may be selected soas to enhance an illusion of a virtual sound source at a given locationin space. Particularly, the predetermined direction of arrival can be ofa wobble shape in which reflection directions slowly evolve away from avirtual sound source and oscillate back and forth. The change inreflection direction imparts a time-varying IACC to the simulatedresponse that varies as a function of time and frequency, which offers anatural sense of space while preserving audio fidelity. Especially, thepredetermined direction of arrival may further include a stochasticdiffuse component within a predetermined azimuths range. As a result, itfurther introduces diffuseness, which provides better externalization.Moreover, the wobble shapes and/or the stochastic diffuse component canbe selected based on a direction of the virtual sound source so that theexternalization could be further improved.

In an embodiment of the present disclosure, during generatingreflections respective occurrence time points of the reflections aredetermined scholastically within a predetermined echo densitydistribution constraint. Then desired directions of the reflections aredetermined based on the respective occurrence time points and thepredetermined directional pattern, and amplitudes of the reflections atthe respective occurrence time points are determined scholastically.Then based on the determined values, the reflections with the desireddirections and the determined amplitudes at the respective occurrencetime points are generated. It should be understood that the presentdisclosure is not limited to the order of operations as described above.For example, operations of determining desired directions anddetermining amplitudes of the reflections can be performed in a reversesequence or performed simultaneously.

In another embodiment of the present disclosure, the reflections at therespective occurrence time points may be created by selecting, fromhead-related transfer function (HRTF) data sets measured for particulardirections, HRTFs based on the desired directions at the respectiveoccurrence time points and then modifying the HRTFs based on theamplitudes of the reflections at the respective occurrence time points

In an alternative embodiment of the present disclosure, creatingreflections may also be implemented by determining HRTFs based on thedesired directions at the respective occurrence time points and apredetermined spherical head model and afterwards modifying the HRTFsbased on the amplitudes of the reflections at the respective occurrencetime points so as to obtain the reflections at the respective occurrencetime points.

In another alternative embodiment of the present disclosure, creatingreflections may include generating impulse responses for two ears basedon the desired directions and the determined amplitudes at therespective occurrence time points and broadband interaural timedifference and interaural level difference of a predetermined sphericalhead model. Additionally, the created impulse responses for two ears maybe further filtered through all-pass filters to obtain further diffusionand decorrelation.

In a further embodiment of the present disclosure, the method isoperated in a feedback delay network. In such a case, the input signalis filtered through HRTFs, so as to control at least directions of earlypart of late responses to meet the predetermined directional pattern. Insuch a way, it is possible to implement the solution in a morecomputationally efficient way

Additionally, an optimal process is performed. For example, generatingreflections may be repeated to obtain a plurality of groups ofreflections and then one of the plurality of groups of reflectionshaving an optimal reflection characteristic may be selected as thereflections for inputting signals. Or alternatively, generatingreflections may be repeated till a predetermined reflectioncharacteristic is obtained. In such way, it is possible to furtherensure that reflections with desirable reflection characteristic areobtained.

It can be understood that for a purpose of simplification, the method asillustrated in FIG. 14 is described in brief; for detailed descriptionof respective operations, one can find in the corresponding descriptionwith reference FIGS. 1 to 13 .

It can be appreciated that although specific embodiments of the presentdisclosure are described herein, those embodiments are only given for anillustration purpose and the present disclosure is not limited thereto.For example, the predetermined directional pattern could be anyappropriate pattern other than the wobble shape or can be a combinationof multiple directional patterns. Filters can also be any other type offilters instead of HRTFs. During generating the reflections, theobtained HRTFs can be modified in accordance with the determinedamplitude in any way other than that illustrated in Eqs. 2A and 2B. Thesummers 121-L and 121-R as illustrated in FIG. 1 can be implemented in asingle general summer instead of two summers. Moreover, the arrangementof the delayer and filter pair can be changed in reverse which meansthat it might require delayers for the left ear and the right earrespectively. Besides, the mixing matrix as illustrated in FIGS. 7 and 8is also possibly implemented by two separate mixing matrixes for theleft ear and the right ear respectively.

In addition, it is to also be understood that the components of any ofthe systems 100, 700, 800, 900, 1000, 1100, 1200 and 1300 may behardware modules or software modules. For example, in some exampleembodiments, the system may be implemented partially or completely assoftware and/or firmware, for example, implemented as a computer programproduct embodied in a computer readable medium. Alternatively oradditionally, the system may be implemented partially or completelybased on hardware, for example, as an integrated circuit (IC), anapplication-specific integrated circuit (ASIC), a system on chip (SOC),a field programmable gate array (FPGA), and the like.

FIG. 15 shows a block diagram of an example computer system 1500suitable for implementing example embodiments of the present disclosure.As shown, the computer system 1500 includes a central processing unit(CPU) 1501 which is capable of performing various processes inaccordance with a program stored in a read only memory (ROM) 1502 or aprogram loaded from a storage unit 1508 to a stochastic access memory(RAM) 1503. In the RAM 1503, data required when the CPU 1501 performsthe various processes or the like is also stored as required. The CPU1501, the ROM 1502 and the RAM 1503 are connected to one another via abus 1504. An input/output (I/O) interface 1505 is also connected to thebus 1504.

The following components are connected to the I/O interface 1505: aninput unit 1506 including a keyboard, a mouse, or the like; an outputunit 1507 including a display such as a cathode ray tube (CRT), a liquidcrystal display (LCD), or the like, and a loudspeaker or the like; thestorage unit 1508 including a hard disk or the like; and a communicationunit 1509 including a network interface card such as a LAN card, amodem, or the like. The communication unit 1509 performs a communicationprocess via the network such as the internet. A drive 1510 is alsoconnected to the I/O interface 1505 as required. A removable medium1511, such as a magnetic disk, an optical disk, a magneto-optical disk,a semiconductor memory, or the like, is mounted on the drive 1510 asrequired, so that a computer program read therefrom is installed intothe storage unit 1508 as required.

Specifically, in accordance with example embodiments of the presentdisclosure, the processes described above may be implemented as computersoftware programs. For example, embodiments of the present disclosureinclude a computer program product including a computer program tangiblyembodied on a machine readable medium, the computer program includingprogram code for performing methods. In such embodiments, the computerprogram may be downloaded and mounted from the network via thecommunication unit 1509, and/or installed from the removable medium1511.

Generally, various example embodiments of the present disclosure may beimplemented in hardware or special purpose circuits, software, logic orany combination thereof. Some aspects may be implemented in hardware,while other aspects may be implemented in firmware or software which maybe executed by a controller, microprocessor or other computing device.While various aspects of the example embodiments of the presentdisclosure are illustrated and described as block diagrams, flowcharts,or using some other pictorial representation, it will be appreciatedthat the blocks, apparatus, systems, techniques or methods describedherein may be implemented in, as non-limiting examples, hardware,software, firmware, special purpose circuits or logic, general purposehardware or controller or other computing devices, or some combinationthereof.

Additionally, various blocks shown in the flowcharts may be viewed asmethod steps, and/or as operations that result from operation ofcomputer program code, and/or as a plurality of coupled logic circuitelements constructed to carry out the associated function(s). Forexample, embodiments of the present disclosure include a computerprogram product including a computer program tangibly embodied on amachine readable medium, the computer program containing program codesconfigured to carry out the methods as described above.

In the context of the disclosure, a machine readable medium may be anytangible medium that may contain, or store a program for use by or inconnection with an instruction execution system, apparatus, or device.The machine readable medium may be a machine readable signal medium or amachine readable storage medium. A machine readable medium may includebut not limited to an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples of the machinereadable storage medium would include an electrical connection havingone or more wires, a portable computer diskette, a hard disk, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), an optical fiber, a portablecompact disc read-only memory (CD-ROM), an optical storage device, amagnetic storage device, or any suitable combination of the foregoing.

Computer program code for carrying out methods of the present disclosuremay be written in any combination of one or more programming languages.These computer program codes may be provided to a processor of a generalpurpose computer, special purpose computer, or other programmable dataprocessing apparatus, such that the program codes, when executed by theprocessor of the computer or other programmable data processingapparatus, cause the functions/operations specified in the flowchartsand/or block diagrams to be implemented. The program code may executeentirely on a computer, partly on the computer, as a stand-alonesoftware package, partly on the computer and partly on a remote computeror entirely on the remote computer or server or distributed over one ormore remote computers and/or servers.

Further, while operations are depicted in a particular order, thisshould not be understood as requiring that such operations be performedin the particular order shown or in sequential order, or that allillustrated operations be performed, to achieve desirable results. Incertain circumstances, multitasking and parallel processing may beadvantageous. Likewise, while several specific implementation detailsare contained in the above discussions, these should not be construed aslimitations on the scope of any invention or of what may be claimed, butrather as descriptions of features that may be specific to particularembodiments of particular inventions. Certain features that aredescribed in this specification in the context of separate embodimentsmay also be implemented in combination in a single embodiment.Conversely, various features that are described in the context of asingle embodiment may also be implemented in multiple embodimentsseparately or in any suitable sub-combination.

Various modifications, adaptations to the foregoing example embodimentsof this invention may become apparent to those skilled in the relevantarts in view of the foregoing description, when read in conjunction withthe accompanying drawings. Any and all modifications will still fallwithin the scope of the non-limiting and example embodiments of thisinvention. Furthermore, other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseembodiments of the invention pertain having the benefit of the teachingspresented in the foregoing descriptions and the drawings.

The present disclosure may be embodied in any of the forms describedherein. For example, the following enumerated example embodiments (EEEs)describe some structures, features, and functionalities of some aspectsof the present disclosure.

EEE1. A method for generating one or more components of a binaural roomimpulse response (BRIR) for headphone virtualization, including:generating directionally-controlled reflections that impart a desiredperceptual cue to an audio input signal corresponding to a sound sourcelocation; and combining at least the generated reflections to obtain theone or more components of the BRIR.

EEE2. The method of EEE1, wherein the desired perceptual cues lead to anatural sense of space with minimal side effects.

EEE 3. The method of EEE 1, wherein the directionally-controlledreflections have a predetermined direction of arrival in which anillusion of a virtual sound source at a given location in space isenhanced.

EEE 4. The method of EEE 3, wherein the predetermined directionalpattern is of a wobble shape in which reflection directions change awayfrom a virtual sound source and oscillate back and forth therearound.

EEE 5. The method of EEE 3, wherein the predetermined directionalpattern further includes a stochastic diffuse component within apredetermined azimuths range, and wherein at least one of the wobbleshapes or the stochastic diffuse components is selected based on adirection of the virtual sound source.

EEE 6. The method of EEE 1, wherein generating directionally-controlledreflections includes: determining respective occurrence time points ofthe reflections scholastically under a predetermined echo densitydistribution constraint; determining desired directions of thereflections based on the respective occurrence time points and thepredetermined directional pattern; determining amplitudes of thereflections at the respective occurrence time points scholastically; andcreating the reflections with the desired directions and the determinedamplitudes at the respective occurrence time points.

EEE 7. The method of EEE 6, wherein creating the reflections includes:

-   -   selecting, from head-related transfer function (HRTF) data sets        measured for particular directions, HRTFs based on the desired        directions at the respective occurrence time points; and        modifying the HRTFs based on the amplitudes of the reflections        at the respective occurrence time points so as to obtain the        reflections at the respective occurrence time points.

EEE 8. The method of EEE 6, wherein creating the reflections includes:determining HRTFs based on the desired directions at the respectiveoccurrence time points and a predetermined spherical head model; andmodifying the HRTFs based on the amplitudes of the reflections at therespective occurrence time points so as to obtain the reflections at therespective occurrence time points.

EEE 9. The method of EEE 5, wherein creating the reflections includes:generating impulse responses for two ears based on the desireddirections and the determined amplitudes at the respective occurrencetime points and based on broadband interaural time difference andinteraural level difference of a predetermined spherical head model.

EEE 10. The method of EEE 9, wherein creating the reflections furtherincludes:

-   -   filtering the created impulse responses for two ears through        all-pass filters to obtain a diffusion and decorrelation.

EEE 11. The method of EEE 1, wherein the method is operated in afeedback delay network, and wherein generating reflections includesfiltering the audio input signal through

-   -   HRTFs, so as to control at least directions of an early part of        late responses to impart desired perceptual cues to the input        signal.

EEE 12. The method of EEE 11, wherein the audio input signal is delayedby delay lines before it is filtered by the HRTFs.

EEE 13. The method of EEE 11, wherein the audio input signal is filteredbefore signals fed back through at least one feedback matrix are added.

EEE 14. The method of EEE 11, wherein the audio input signal is filteredby the HRTFs in parallel with the audio input signal being inputted intothe feedback delay network, and wherein output signals from the feedbackdelay network and from the HRTFs are mixed to obtain the reverberationfor headphone virtualization.

EEE15. The method of EEE11, wherein for multiple audio channels orobjects, an input audio signal for each of the multiple audio channelsor objects is separately filtered by the HRTFs.

EEEE16. The method of EEE 11, wherein for multiple audio channels orobjects, input audio signals for the multiple audio channels or objectsare downmixed and analyzed to obtain an audio mixture signal with adominant source direction, which is taken as the input signal.

EEE17. The method of EEE1, further including performing an optimalprocess by:

-   -   repeating the generating reflections to obtain a plurality of        groups of reflections and selecting one of the plurality of        groups of reflections having an optimal reflection        characteristic as the reflections for the input signal; or        repeating the generating reflections till a predetermined        reflection characteristic is obtained.

EEE18. The method of EEE17, wherein the generating reflections is drivenin part by at least some of the random variables generated based on astochastic mode.

It will be appreciated that the embodiments of the present invention arenot to be limited to the specific embodiments as discussed above andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areused herein, they are used in a generic and descriptive sense and arenot for purposes of limitation.

1. A system, comprising: a filtering unit configured to convolve a pairof binaural room impulse responses, BRIRs, containing directionallycontrolled reflections that impart a desired perceptual cue, with anaudio input signal to produce a set of left-ear and right-earintermediate signals, wherein the directionally controlled reflectionshave a directional pattern in which a direction of arrival changes as afunction of time; a stochastic echo generator configured to generatecoefficients for the filtering unit for adding a stochastic component tothe BRIRs; and a combining unit configured to receive the intermediatesignals and combine them to form a binaural output signal.
 2. The systemof claim 1, wherein the audio input signal corresponds to a sound sourcelocation, and wherein the directional pattern describes how directionsof arrival of the directionally-controlled reflections change inrelation to a direction of the sound source location as a function oftime.
 3. The system of claim 1, wherein coefficients for the filteringunit are derived from a Head-Related Transfer Function (HRTF) data set,where each filter of the filtering unit provides perceptual cuescorresponding to one reflection from a predetermined direction for botha left ear and a right ear.
 4. The system of claim 1, wherein thecombining unit comprises a left summer and a right summer, wherein allleft-ear intermediate signals are mixed in the left summer to produce aleft binaural output signal, and all right-ear intermediate signals aremixed in the right summer to produce a right binaural output signal. 5.A method, comprising: convolving, using a filtering unit, a pair ofbinaural room impulse responses, BRIRs, containing directionallycontrolled reflections that impart a desired perceptual cue, with anaudio input signal to produce a set of left-ear and right-earintermediate signals, wherein the directionally controlled reflectionshave a directional pattern in which a direction of arrival changes as afunction of time; generating coefficients for the filtering unit foradding a stochastic component to the BRIRs; and combining theintermediate signals to form a binaural output signal.
 6. The method ofclaim 5, wherein the audio input signal corresponds to a sound sourcelocation, and wherein the directional pattern describes how directionsof arrival of the directionally-controlled reflections change inrelation to a direction of the sound source location as a function oftime.
 7. The method of claim 5, wherein coefficients for the filteringunit are derived from a Head-Related Transfer Function (HRTF) data set,where each filter of the filtering unit provides perceptual cuescorresponding to one reflection from a predetermined direction for botha left ear and a right ear.
 8. A computer program product havinginstructions which, when executed by a computing device or system, causesaid computing device or system to perform the method according to claim5.